Polyester films have been used in various applications such as touch panels, prism lens films, micro-lens films, light diffusion films, anti-reflective films, hard coat films, electromagnetic shielding films, molding base materials or the like because of excellent transparency and strength thereof. In recent years, it has been required that the polyesters films, in particular, those polyester films used in the applications in which a surface functional layer such as a hard coat layer should be formed thereon, such as members of displays for touch panels, in-mold transfer films and in-mold label films, have a more excellent transparency.
Conventionally, there is generally known the method in which particles are incorporated into a polyester film for the purpose of imparting a good easy-slipping property to the film (Patent Documents 1 and 2). However, in the case where the particles are incorporated into the polyester film, the resulting film tends to exhibit a high haze and therefore tends to have a whitish appearance, or tends to have a feel of grains due to the particles incorporated therein and therefore tends to be deteriorated in visibility when viewed under a fluorescent lamp.
To solve these problems, there has been proposed a polyester film comprising no particles (Patent Document 3). However, the polyester film comprising no particles tends to have such a drawback that the film has a poor slipping property and therefore is readily injured. There has been proposed the method in which a coating layer comprising particles is formed on a monoaxially stretched polyester film to impart a slip property thereto. However, the polyester film is not improved in slip property before forming the coating layer thereon, and therefore tends to be unavoidably injured owing to the poor slip property between the step of forming the film by melt-extrusion and the step of applying the coating solution thereto.